Crystalline-amorphous inks, sometimes referred to as phase-change inks, are known as one alternative for solid ink jet printing. Some known phase-change ink designs use a mixture of crystalline and amorphous materials. The crystalline material imparts a hardness and rapid phase change that is required for DTP (direct-to-paper) print architectures. The amorphous material (typically a viscous, tacky material) aids in adhesion to the substrate and plasticizes the crystalline component to prevent embrittlement and cracking of the printed image.
Thus far, many amorphous and crystalline materials have been developed. To date, the amorphous materials have almost exclusively been comprised of esters. One known amorphous component is a derivative of L-tartaric acid/cyclohexanol/tBu cyclohexanol (“TBCT”), which is considered to contribute to acceptable robust images. However, TBCT suffers from several disadvantages, such as thermal stability during synthesis and variation in product distributions, both of which pose challenges for scale-up synthesis. Furthermore, inks containing TBCT do not meet rub resistance requirements for finishing.
Ureas are generally known in the chemical industry as the strongest hydrogen bonding materials in the functional group series of carbonates, esters, urethanes, and amides. Ureas are also known to be less prone to hydrolysis than these other compounds. Owing to the strong hydrogen bonding, ureas tend to be very viscous. For this reason, many if not most ureas would be considered unsuitable for use as inks for inkjet printing, since inkjet printing technology generally employs inks having relatively low viscosities at printer operating temperatures.
It would be considered an advancement in the art to provide novel classes of materials that are suitable for use as the amorphous component in crystalline-amorphous phase-change inks.